Fix escaping of bookmarknames properly for arc patch

Summary:
Fixes T4596. I misunderstood this issue and D8512 was not correct. Specifically:

• The hg log needs to be escaped, since otherwise "arcpatch-x" is interpreted as a revset.
• The hg update does not need to be escaped, since updating to a revset doesn't make sense and the command never treats its argument as a revset.
• The hg bookmark does not need to be escaped, for similar reasons.

Test Plan:

• Ran these commands in isolation and got sensible, consistent results.
• Ran arc patch several times in a row and got proper bookmark names.

Reviewers: btrahan, durham, rvanvelzen

Reviewed By: rvanvelzen

Subscribers: epriestley

Maniphest Tasks: T4596

Differential Revision: https://secure.phabricator.com/D8661