archivematicaClient: improve error reporting
archivematicaClient: improve error reporting

The generic exception case was printing the __str__() representation
of an exception tuple from sys.exc_info(), which turns out to be not
very useful. Similarly, the OSError case was printing the __str__()
representation of the exception object, which prints only the message
and not the backtrace.

Compare before:

(<type 'exceptions.UnicodeDecodeError'>, UnicodeDecodeError('ascii', '--transferUUID "ab9f8be4-f7e8-43b2-9f80-1a8078a45d18" --sipDirectory "/var/archivematica/sharedDirectory/currentlyProcessing/unicode49-ab9f8be4-f7e8-43b2-9f80-1a8078a45d18/" --filePath "/var/archivematica/sharedDirectory/currentlyProcessing/unicode49-ab9f8be4-f7e8-43b2-9f80-1a8078a45d18/objects/\xe3\x80\x90\xe7\xa5\x9e\xe6\x9b\xb2\xe3\x80\x91\xe3\x83\x86\xe3\x82\xa4\xe3\x83\xab\xe3\x82\xb3\xe3\x83\xb3\xe3\x83\x81\xe3\x82\xa7\xe3\x83\xab\xe3\x83\x88\xe4\xb8\xbb\xe9\xa1\x8c\xe6\xad\x8c\xe3\x80\x8eFor LITTLE TAIL\xe3\x80\x8f.mp3" --fileUUID "None" --eventIdentifierUUID "%taskUUID%" --date "2013-09-25T23:47:20.335850"', 296, 297, 'ordinal not in range(128)'), <traceback object at 0x166e5a8>)

to after:

Traceback (most recent call last):
  File "/usr/lib/archivematica/MCPClient/archivematicaClient.py", line 141, in executeCommand
    arguments = arguments.replace ( key, replacementDic[key] )
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe3 in position 296: ordinal not in range(128)

refs #5668.

sevein/archivematica,artefactual/archivematica,eckardm/archivematica,sevein/archivematica,artefactual/archivematica,sevein/archivematica,michal-ruzicka/archivematica,eckardm/archivematica,artefactual/archivematica,eckardm/archivematica,michal-ruzicka/archivematica,eckardm/archivematica,sevein/archivematica,artefactual/archivematica,michal-ruzicka/archivematica,michal-ruzicka/archivematica