modprobe: add --all=modules.load flag

Add a means to specify the modules to load from a file, rather than
on the argument list by adding an optional argument to the --all flag.
This allows modprobe to be designated as a standalone service to load
a long series of modules in the background and be specified
separately.  The specified (module.load) file contains a newline
separate list of module names, and supports line comments using '#'
since this file may be maintained by a human or scripting that
requires tagging for regions of the file.

Bug: 159424228
Bug: 151950334
Test: use modprobe as a service to load modules
Change-Id: Id32641c7244e65848fca3a4a82c8d08b2042bf2f