Remove in-place try/except blocks from shell commands

Currently we have try/except blocks for each shell command which
may cause an exception, and often we unaware of all possible
exceptions. Therefore our in-place messages may not correspond
to real server exceptions. This patch removes in-place handlers
so shell will rely on single try/except based in
/ironicclient/shell.py: main, which simply prints server's
exception message.

Change-Id: I65dc71c6fb15483fb88ef4c6a423147fe0bb54cb
Closes-Bug: #1251712
Merge "Remove in-place try/except blocks from shell commands"