[true-hitless] make service script release separately

Hitless config service will priorize /var/google version script first,
then the script on the SPI. The first is released non-disruptively and
does not need firmware update.

Tested: with cl/842939290

Dec 07 01:10:14 dddhg23-nfd01.prod.google.com true-hitless-exec-wrapper.sh[4199]: Execute from /var/google/true-hitless/emmc-true-hitless-enable.sh
Dec 07 01:10:14 dddhg23-nfd01.prod.google.com true-hitless-exec-wrapper.sh[4206]: True-hitless is enabled
Dec 07 01:10:14 dddhg23-nfd01.prod.google.com true-hitless-exec-wrapper.sh[4206]: Starting emmc-available postprocessing...
Dec 07 01:10:18 dddhg23-nfd01.prod.google.com true-hitless-exec-wrapper.sh[4206]: Running version compatibility check...
Dec 07 01:10:18 dddhg23-nfd01.prod.google.com true-hitless-exec-wrapper.sh[4221]: Execute from /var/google/true-hitless/true-hitless-version-check.sh

Fusion-Link: fusion2 N/A not covered
Google-Bug-Id: 467387324
Change-Id: I1ef8277837ff5e591cc691f766e4098ba4e79a38
Signed-off-by: Yuxiao Zhang <yuxiaozhang@google.com>