Add -f and -o options to ifmap-view for xml output/write to file

Defaults remain as-is (human readable on stdout).
    ifmap_view.py localhost 8443 visual visual -o foo -f xml
writes indented xml received from ifmap server to file called 'foo'.

Change-Id: Ia680d7ba87c45b88716140b5b5bf578488db1ab7
Partial-Bug: #1392595
Merge "Add -f and -o options to ifmap-view for xml output/write to file"