Support dynamic user to run alluxio
Support dynamic user to run alluxio

The issue is that alluxio docker image only supports two users: alluxio
and root, but in the customer env, they have more users and the data of
each user are isolated. So we need to make alluxio docker image can
support run container by specifying during running time.

This feature by default is disabled.

pr-link: Alluxio/alluxio#12104
change-id: cid-37cd7ac23075b398b428434f12bf0169710fd3d9
wwjiang007/alluxio,maobaolong/alluxio,EvilMcJerkface/alluxio,maobaolong/alluxio,wwjiang007/alluxio,calvinjia/tachyon,maobaolong/alluxio,Alluxio/alluxio,calvinjia/tachyon,calvinjia/tachyon,Alluxio/alluxio,bf8086/alluxio,wwjiang007/alluxio,maobaolong/alluxio,Alluxio/alluxio,EvilMcJerkface/alluxio,EvilMcJerkface/alluxio,maobaolong/alluxio,calvinjia/tachyon,bf8086/alluxio,Alluxio/alluxio,EvilMcJerkface/alluxio,Alluxio/alluxio,bf8086/alluxio,maobaolong/alluxio,calvinjia/tachyon,wwjiang007/alluxio,Alluxio/alluxio,bf8086/alluxio,EvilMcJerkface/alluxio,calvinjia/tachyon,Alluxio/alluxio,wwjiang007/alluxio,calvinjia/tachyon,calvinjia/tachyon,bf8086/alluxio,EvilMcJerkface/alluxio,Alluxio/alluxio,bf8086/alluxio,wwjiang007/alluxio,maobaolong/alluxio,EvilMcJerkface/alluxio,maobaolong/alluxio,wwjiang007/alluxio,wwjiang007/alluxio,Alluxio/alluxio,wwjiang007/alluxio,maobaolong/alluxio,EvilMcJerkface/alluxio,Alluxio/alluxio,bf8086/alluxio,bf8086/alluxio,wwjiang007/alluxio,maobaolong/alluxio