Support go 1.12

go 1.12 changed the stack trace of a function call during global
variable initialization to contain a function called
"PKG.init.ializers".  Fix callerName to split the package path
and function name on the first "." after the last "/", and look
for functions called "init.ializers" or functions with the
prefix "init."

Test: Soong tests with go 1.12
Change-Id: I25f1ba989ef2d65ca85cb7c9d84454cca230ff86