Better report too large pack-files from PushCommand

Better report too large pack-files from PushCommand

JGits PushCommand and BasePackPushConnection were throwing generic
TransportExceptions when the pushed pack-file was rejected by the server
since it was too big. Let JGit better interprete the server's response
to detect this situation and throw a more specific exception.

This detection works by parsing the status line sent by the server. This
change only recognizes the response sent by a JGit based server. All
other servers which report such problems in a different way still lead
to a generic TransportExceptions.

Change-Id: Ic075764ea152939ce72c446252464620dd54edea
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>