Add option to start-impala-cluster to only restart impalad
Add option to start-impala-cluster to only restart impalad

This helps speed up the restart time becuase we don't need to restart
the catalog server and reload the table metadata. This is useful if you
want to restart the impalad with a different command line parameter
or if you are making changes to only the impalad binary.

Change-Id: I0b714afaf7e508c450a353a53d67d95165de3486
Reviewed-on: http://gerrit.ent.cloudera.com:8080/897
Reviewed-by: Lenni Kuff <724b7df200764f5dc1b723c05ee6c6adabd11bb1@cloudera.com>
Tested-by: jenkins

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