escape all chars other than a-z,A-Z,digits in kmcAction setpasshashkey

PLAT-1728 #time 20m
allow only base64_encode chars in setpasshashkey
define regex as const
fixing regex name
check valid expression with base64 chars
bug fix
assign hash key & saving function call
Merge pull request #1584 from kaltura/IX-9.19.2-PLAT-1728

escape all chars other than a-z,A-Z,digits in kmcAction setpasshashkey