Fix the unlimited length of console-log

Since the commit Idf88a238d1b0e545ebab5be872269b1b1030cc56 of Nova,
the unlimited length has been changed to -1 for API consistency.

This patch applies it to novaclient.

Change-Id: I581609a55f081184ad9d791ba38d78fa30d298a6
Closes-Bug: #1295426
Merge "Fix the unlimited length of console-log"