Revert "Use only awk for umount match"

This reverts commit 21474a6e887f42592f49215ad41a7184d0f43f87.

This patch has some weird problem with the grep I don't understand,
so I'm backing it out.

ONIE:/ # sh -x onl-10183fe-powerpc-all.2014.10.05.03.52.installer
[snip]
+ echo Platform installer version: unknown
Platform installer version: unknown
+ platform_installer
+ installer_standard_blockdev_install sda 16M 64M
+ local blockdev=sda
+ local p1size=16M
+ local p2size=64M
+ local p3size=
+ installer_blockdev_format sda 16M 64M
+ local blockdev=sda
+ local partition1size=16M
+ local partition2size=64M
+ local partition3size=
+ installer_umount_blockdev sda
+ local blockdev=sda
+ echo Test Robs 0
Test Robs 0
+ grep sda /proc/mounts
onl-10183fe-powerpc-all.2014.10.05.03.52.installer: line 1: syntax error: unterminated quoted string
Merge branch 'master' of github.com:capveg/ONL