Fixing grep in validate mount point

When we look for the mount point of a labeled partition it can
happen that the grep command reports more than one mount point
because the devices start with the same path.

As an example, let's consider /dev/vda1, assigned from the
command ``/sbin/blkid | grep 'ephemeral0' | cut -d':'``
If we now call the ``mount`` command and grep for that
device, we actually get 2 different mount point:
sudo mount | grep '/dev/vda1' | cut -d' ' -f1
/dev/vda1
/dev/vda15

This output will make the test fail.

As a fix, we call the grep command with the -w option that match
only entire words:
sudo mount | grep -w '/dev/vda1' | cut -d' ' -f1
/dev/vda1

Change-Id: I2eaad4c91d9beec7077fb71186713e552afaa11a
1 file changed