Extract public key ID from cert

Extracts keyid inline using openssl commands.
The keyid is passed as one of the kernel command line parameters
for the dm-android-verity module to mount root fs(system)
with verity enabled.

(cherry-picked from 3af315ae
https://googleplex-android-review.git.corp.google.com/#/c/1061691/)

BUG: 28384658
Change-Id: I8efbe1b0e415ef1d396f9b51cfa4b3fa01b22484