Retry valgrind curl command via script instead of --retry

[eramongodb]

Followup to #1383 to address spurious task failure due to the following error:

curl: (16) Error in the HTTP2 framing layer

curl does not appear to --retry for this error code. Considered using --retry-all-errors, but docs state:

This option is the "sledgehammer" of retrying. Do not use this option by default (for example in your curlrc), there may be unintended consequences such as sending or receiving duplicate data. Do not use with redirected input or output. You'd be much better off handling your unique problems in shell script. Please read the example below.

Therefore, applied the suggestion to handle the problem via shell script by using a simple for loop in Bash instead of --retry 5. The subsequent sha1sum command will fail if the curl command did not succeed with either:

sha1sum: valgrind-3.24.0.tar.bz2: No such file or directory
sha1sum: WARNING: 1 listed file could not be read

or:

sha1sum: WARNING: 1 computed checksum did NOT match