Image doesn't contain "which" command

[grozeille]

When restarting the services after deployment, it fails with the error message:

resource_management.core.exceptions.Fail: Execution of 'ambari-sudo.sh su hdfs -l -s /bin/bash -c 'ulimit -c unlimited ;  /usr/hdp/current/hadoop-client/sbin/hadoop-daemon.sh --config /usr/hdp/current/hadoop-client/conf start namenode'' returned 1. starting namenode, logging to /var/log/hadoop/hdfs/hadoop-hdfs-namenode-hdp-ambari-agent-namenode-1.out
/usr/hdp/2.6.1.0-129//hadoop-hdfs/bin/hdfs.distro: line 28: which: command not found
dirname: missing operand
Try 'dirname --help' for more information.

which command is needed in the image

[grozeille]

I confirm that I can upgrade the hdfs configuration in Ambari with this pull request: #136