Error handling improvements in rabbit_epmd_monitor:check_epmd/1

[michaelklishin]

Proposed Changes

This slightly improves error handling improvements in rabbit_epmd_monitor:check_epmd/1.

To produce less noise and more informative messages.
This also introduces a function that allows for manual
check triggering.

Types of Changes

• Bug fix (non-breaking change which fixes issue Handle more errors in rabbit_epmd_monitor #2130)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

Closes #2130.

[lukebakken]

👍

Commit ef580fb changes the output from this:

2019-10-03 09:00:02.487 [debug] <0.528.0> Asked to [re-]register this node (rabbit@"MESSIAEN") with epmd...
(rabbit@MESSIAEN)2> 2019-10-03 09:00:02.634 [debug] <0.528.0> [Re-]registered this node (rabbit@"MESSIAEN") with epmd at port 25672

to this (no extra double-quotes):

2019-10-03 09:01:36.709 [debug] <0.407.0> Asked to [re-]register this node (rabbit@MESSIAEN) with epmd...
(rabbit@MESSIAEN)2> 2019-10-03 09:01:36.860 [debug] <0.407.0> [Re-]registered this node (rabbit@MESSIAEN) with epmd at port 25672

[lukebakken]

Backported to v3.8.x

[lukebakken]

Backported to v3.7.x