GEODE-6796: Specially-handle UnknownHostException in jmxConnect()

[jackw26]

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[onichols-pivotal]

@metatype commented (on dev list) "I don’t agree that adding the exception class name creates a better user experience."

[jinmeiliao]

Only in this case, it probably does offer more information if the message itself has typo's that doesn't make any sense. Another way to fix this is to check if the message itself has "nor servname" string, if so, give it another message that makes sense.

[jinmeiliao]

Oh, I think there is a better solution here, in StartLocatorCommand, you can catch the UnknownHostException specifically and provide a more sensible error message, and the leave the general exception catch block the same as before.

[onichols-pivotal]

@jinmeiliao What qualifies as "more sensible"? If we are not going to print the exception's message, then we lose the information about exactly what hostname was not found...

Do any of these look better?

#1 (generic)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
Unable to connect.

#2 (Safari)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
Can't find the server.

#3 (golang)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
dial tcp l192.168.99.1:12345: i/o timeout

#4 (Chrome)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
Locator can't be reached. Server or IP address could not be found.

#5 (Firefox)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
The proxy server is refusing connections.

#6 (Zero Wing)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
All your server are belong to us.

#7 (2001 A Space Odyssey)
Connecting to Locator at [host=l192.168.99.1, port=12345] ..
I'm sorry, Dave. I'm afraid I can't do that.

[onichols-pivotal]

PR has been updated to revert the first approach and go with option #4 instead. Now the user will see:
Connecting to Locator at [host=l192.168.99.1, port=52326] ..
JMX manager can't be reached. Hostname or IP address could not be found.