Functionbeat keystore is not packaged

[kvch]

Version: master

Steps to reproduce:

$ ./functionbeat keystore create
$ ./functionbeat keystore add ES_PWD
$ ./functionbeat package

Keystore file is missing:

$ unzip -l package.zip
Archive:  package.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
     1332  1980-00-00 00:00   functionbeat.yml
 67144240  1980-00-00 00:00   functionbeat
---------                     -------
 67145572                     2 files

The issue has two parts. First, the keystore file cannot be found, thus keystoreRaw returns a zero lenght byte slice. If that's fixed, the path of the file needs to be changed from the hard coded data/functionbeat.keystore to the one configured in functionbeat.yml.