Fix misspellings in devstack gate

Fix misspellings detected by:
* pip install misspellings
* git ls-files | grep -v locale | misspellings -f -

Change-Id: Ib63929e6e7c01f4c422edef9bad421b1252609a3
Closes-Bug: #1257295
Merge "Fix misspellings in devstack gate"