Remove leading spaces from the CLI command before parsing

If you've mistakenly put a space before typing in a command, the
leading space will be included as part of the command, and the command
parser will not find the corresponding command. This patch rectifies
that situation by stripping the leading spaces on commands.

Review: https://reviewboard.asterisk.org/r/2709/
Patch-by: Tilghman Lesher


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@396745 f38db490-d61c-443f-a65b-d21fe96a405b