force_navigate is less grabby

I went through the selenium exceptions, and found a WebDriverError subclass
that's likely good for our needs without supressing other "legitimate"
WebDriver errors, like state elements or element not found.

I also tweaked test generation in test_nav while testing this change, because
the nav destination names make more sense than the string versions of the menu
entries (in my opinion, at least).
Added possibility to use start= in force_navigate correctly

Conflicts:
	cfme/fixtures/pytest_selenium.py
Made RHEV delete a little more robust
Merge pull request #628 from seandst/force-navigate-eats-less-errors

force_navigate is less grabby
Ability to tell force_navigate to restart navigation by raising a specific exception
Reduced number of tries by 1
Merge pull request #631 from psav/update_rhev_delete

Made RHEV delete a little more robust
Merge pull request #640 from mfalesni/force_navigate-forced_recyclation

Ability to tell force_navigate to restart navigation from beginning by raising a specific exception
mfalesni made a boo-boo
Merge pull request #641 from mfalesni/force_navigate-forced_recyclation

mfalesni made a boo-boo
Unicode in TB fix
Merge pull request #642 from psav/fix_tb

Unicode in TB fix
Fix Tree same-name issue
* Problem was despite knowing the full path, click_path would click the
  wrong element if there was a node with the same name elsewhere in the
  tree.
* Came down to not being able to use "//" in xpath even when searching
  from a parent node.  Have to use ".//".
Merge branch 'tree-fix' into automate4
Instance class and CRUD tests