Fix H302 violations in plugins package

H302 violation is reported by flake8 when importing separated objects from
modules instead of importing the whole module.
e.g.   from package.module import function
       function()
is changed to
       from package import module
       module.function()

Change-Id: I83372124f4fba7b94bbfb4a56a0c0ef779ee237f
Partial-Bug: #1291032
Merge "Fix H302 violations in plugins package"