Update emr script
Update emr script

allow empty ufs uri (means local hdfs mount)
-c flag which installs client jar and conf but do not start alluxio

The reason for these changes:
1. so that we can launch an emr cluster where the hdfs of that cluster
is mounted as root mount
2. so that we can load jars on to a cluster that does not need alluxio
running. In this case, a hive metastore containing alluxio uris.

pr-link: Alluxio/alluxio#11545
change-id: cid-b0fb71e450668b8f82b4cbea342f5b1dd3f9ba07
Alluxio/alluxio,maobaolong/alluxio,Alluxio/alluxio,maobaolong/alluxio,wwjiang007/alluxio,maobaolong/alluxio,maobaolong/alluxio,wwjiang007/alluxio,bf8086/alluxio,calvinjia/tachyon,EvilMcJerkface/alluxio,Alluxio/alluxio,calvinjia/tachyon,wwjiang007/alluxio,bf8086/alluxio,maobaolong/alluxio,EvilMcJerkface/alluxio,EvilMcJerkface/alluxio,Alluxio/alluxio,Alluxio/alluxio,EvilMcJerkface/alluxio,calvinjia/tachyon,wwjiang007/alluxio,bf8086/alluxio,Alluxio/alluxio,Alluxio/alluxio,calvinjia/tachyon,maobaolong/alluxio,calvinjia/tachyon,wwjiang007/alluxio,bf8086/alluxio,bf8086/alluxio,maobaolong/alluxio,EvilMcJerkface/alluxio,wwjiang007/alluxio,wwjiang007/alluxio,EvilMcJerkface/alluxio,EvilMcJerkface/alluxio,maobaolong/alluxio,calvinjia/tachyon,Alluxio/alluxio,Alluxio/alluxio,bf8086/alluxio,maobaolong/alluxio,bf8086/alluxio,Alluxio/alluxio,calvinjia/tachyon,wwjiang007/alluxio,maobaolong/alluxio,bf8086/alluxio,wwjiang007/alluxio,wwjiang007/alluxio,EvilMcJerkface/alluxio,calvinjia/tachyon