fix: address panic in dfx replica command

[p-shahi]

The dfx replica command panics because it tries to write the replica-pid to a nonexistent replica-configuration directory

Before:

dfx replica
  Version v0.6.20-15-gb2eab11 installed successfully.
thread 'replica-actor' panicked at 'Could not write to replica-pid file.: Os { code: 2, kind: NotFound, message: "No such file or directory" }', src/dfx/src/actors/replica.rs:290:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Jan 27 23:11:00.823 INFO ic-starter. Configuration: ValidatedConfig { replica_path: Some("/Users/prithvishahi/.cache/dfinity/versions/0.6.20-15-gb2eab11/replica"), replica_version: "0.1.0", log_level: Warning, subnet_id: fscpm-uiaaa-aaaaa-aaaap-yai, cargo_bin: "cargo", cargo_opts: "", state_dir: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state", http_listen_addr: V4(127.0.0.1:8080), http_port_file: None, metrics_addr: None, hypervisor_create_funds_whitelist: "*", artifact_pool_dir: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/node-100/ic_consensus_pool", crypto_root: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/node-100/crypto", state_manager_root: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/node-100/state", registry_file: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/registry.proto", bootstrap_registry: None, state_dir_holder: None }, Application: starter
Jan 27 23:11:00.823 INFO Initialize replica configuration "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/ic.json5", Application: starter
Jan 27 23:11:00.842 INFO Executing "/Users/prithvishahi/.cache/dfinity/versions/0.6.20-15-gb2eab11/replica" "--replica-version" "0.1.0" "--config-file" "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/ic.json5", Application: starter
Jan 27 23:11:01.891 ERRO s:fscpm-uiaaa-aaaaa-aaaap-yai/n:inmtb-omw6w-7ek54-igna6-ygf5t-hw56y-qn4uj-ighc2-wm45g-mvf2u-2ae/ic_messaging/xnet_endpoint No XNet configuration for node inmtb-omw6w-7ek54-igna6-ygf5t-hw56y-qn4uj-ighc2-wm45g-mvf2u-2ae. This is an error in production, but may be ignored in single-subnet test deployments.
Jan 27 23:11:02.894 WARN s:fscpm-uiaaa-aaaaa-aaaap-yai/n:inmtb-omw6w-7ek54-igna6-ygf5t-hw56y-qn4uj-ighc2-wm45g-mvf2u-2ae/ic_http_handler/ic_http_handler NNS subnet not found in network topology. Skipping fetching the delegation.
^CStopping the replica...
Stopped.

After:

dfx replica
Jan 27 23:29:44.273 INFO ic-starter. Configuration: ValidatedConfig { replica_path: Some("/Users/prithvishahi/.cache/dfinity/versions/0.6.21-dirty/replica"), replica_version: "0.1.0", log_level: Warning, subnet_id: fscpm-uiaaa-aaaaa-aaaap-yai, cargo_bin: "cargo", cargo_opts: "", state_dir: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state", http_listen_addr: V4(127.0.0.1:8080), http_port_file: None, metrics_addr: None, hypervisor_create_funds_whitelist: "*", artifact_pool_dir: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/node-100/ic_consensus_pool", crypto_root: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/node-100/crypto", state_manager_root: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/node-100/state", registry_file: "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/registry.proto", bootstrap_registry: None, state_dir_holder: None }, Application: starter
Jan 27 23:29:44.273 INFO Initialize replica configuration "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/ic.json5", Application: starter
Jan 27 23:29:44.294 INFO Executing "/Users/prithvishahi/.cache/dfinity/versions/0.6.21-dirty/replica" "--replica-version" "0.1.0" "--config-file" "/Users/prithvishahi/dev/ic-projects/tmp/hello/.dfx/state/replicated_state/ic.json5", Application: starter
Jan 27 23:29:45.549 ERRO s:fscpm-uiaaa-aaaaa-aaaap-yai/n:jgers-sv5te-lhyuh-5mgor-6jx2b-5j22n-yrl4c-n22a7-4sfy7-xbbmh-6qe/ic_messaging/xnet_endpoint No XNet configuration for node jgers-sv5te-lhyuh-5mgor-6jx2b-5j22n-yrl4c-n22a7-4sfy7-xbbmh-6qe. This is an error in production, but may be ignored in single-subnet test deployments.
Jan 27 23:29:46.554 WARN s:fscpm-uiaaa-aaaaa-aaaap-yai/n:jgers-sv5te-lhyuh-5mgor-6jx2b-5j22n-yrl4c-n22a7-4sfy7-xbbmh-6qe/ic_http_handler/ic_http_handler NNS subnet not found in network topology. Skipping fetching the delegation.
^CStopping the replica...
Stopped.