Prefer single-quoted strings

* change "" to '' where interpolation is not used
* add missed spaces for {}

Change-Id: I4ba412272212510ea58fe2cec3a16b25ccdd52a7
Reviewed-on: http://review.couchbase.org/26618
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>