Change start-impala-cluster.py to append daemon args
Change start-impala-cluster.py to append daemon args

start-impala-cluster.py takes arguments to pass through to
impalads, catalogd, and statestored, but all arguments must
be passed as a single string today. This changes the arg
parsing to also accept multiple arguments passed as
different parameters.

E.g. the following previously (and still) works:
> start-impala-cluster.py --impalad_args="-v=2 -memlimit=1G"

Now args can optionally be passed separately:
> start-impala-cluster.py --impalad_args=-v=2 --impalad_args=-memlimit=1G

This is helpful in general, but is needed to enable passing
through some arguments from environment variables in jenkins
jobs.

Change-Id: I32f7a75ec4ce8f5ce878b3e7f76880a731842c14
Reviewed-on: http://gerrit.cloudera.org:8080/510
Reviewed-by: Dan Hecht <20ebd99959f0f6e5dcb0fc319b4d8ef53a16b5fb@cloudera.com>
Reviewed-by: Casey Ching <77bc9a9984e6786c5799d7a71768cf023120ef76@cloudera.com>
Reviewed-by: Matthew Jacobs <df2fa7c39d141dc5dc5589fed74180e757ed6c9a@cloudera.com>
Tested-by: Internal Jenkins

cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala