Log err.reason when no err.code is availiable

[zbycz]

When connecting to https resource, the error can have no code. Lets display err.reason instead

ie.:

err { Error: Hostname/IP doesn't match certificate's altnames: "Host: localhost. is not in the cert's altnames: DNS:..."
    at Object.checkServerIdentity (tls.js:222:17)
    at TLSSocket.<anonymous> (_tls_wrap.js:1109:29)
    at emitNone (events.js:106:13)
    at TLSSocket.emit (events.js:208:7)
    at TLSSocket._finishInit (_tls_wrap.js:637:8)
    at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:467:38)
  reason: 'Host: localhost. is not in the cert\'s altnames: DNS:...,
  host: 'localhost',
  cert: ...

Otherwise the log looks like this: (see (undefined))

[HPM] Error occurred while trying to proxy request /url/sth/sth from localhost:3009 to https://example.com (undefined) (https://nodejs.org/api/errors.html#errors_common_system_errors)

[coveralls]

Coverage remained the same at 97.067% when pulling 1e8d788 on zbycz:patch-1 into 952c1af on chimurai:master.

[brettdh]

Maintainers, please review and merge; I struggled with this today and ended up tracking down the same issue and locally fixing to diagnose the same cert issue (missing "changeOrigin": true in config).

[chimurai]

merged in #263