dumpStorageTable: Avoid an unnecessary traceback if vdsmd is down.

When vdsmd is down the first getConnectedStoragePoolsList call
results in a 'Connection Refused' trace being shown. To avoid
this trace being picked up by abrt and thus worrying users we
should test the connection, catching any errors before continuing.

Change-Id: I6d3c0758d9580bfaf164bb3f706d91d8b0ab7f33
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=987833
Signed-off-by: Lee Yarwood <lyarwood@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17278
Reviewed-by: Pavel Zhukov <pzhukov@redhat.com>
Reviewed-by: Tomáš Došek <tdosek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>