Improve error messages

[findepi]

Sometimes messages returned from jgit are less useful and chained cause is more informative

ex -- Invalid remote: origin (propagated to query failure)

...
Caused by: org.eclipse.jgit.api.errors.InvalidRemoteException: Invalid remote: origin
	at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:246)
	at org.eclipse.jgit.api.CloneCommand.fetch(CloneCommand.java:319)
	at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:189)
	at pl.net.was.trino.git.GitRecordSet.getRepo(GitRecordSet.java:115)
	... 34 more
Caused by: org.eclipse.jgit.errors.NoRemoteRepositoryException: /path/to/repo: not found.
	at org.eclipse.jgit.transport.TransportLocal$1.open(TransportLocal.java:100)
	at org.eclipse.jgit.transport.TransportBundleFile$1.open(TransportBundleFile.java:74)
	at org.eclipse.jgit.transport.Transport.open(Transport.java:527)
	at org.eclipse.jgit.transport.Transport.open(Transport.java:402)
	at org.eclipse.jgit.transport.Transport.open(Transport.java:281)
	at org.eclipse.jgit.transport.Transport.open(Transport.java:249)
	at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:217)
	... 37 more

loosely related to #12