netd: all: use system() instead of logwrap() for now.

The logwrapper uses a blocking read() which does not always
correctly detect when the child process at the other end is gone.
This is a quick workaround for http://b/5144246


A cleaner logwrapper parent() will follow.

Add support for BandwidthController() to use either system() or
logwrap(). It looks at "persist.bandwidth.uselogwrap" to be 0 or 1.

Change-Id: I2d17732214f1a7fef6838eee05d827695b707ab0
Signed-off-by: JP Abgrall <jpa@google.com>