Added git update command to clone, checkout, and pull all repositories for use by CI server.
Added git update command to clone, checkout, and pull all repositories for use by CI server.

mpouttuclarke/cdap,mpouttuclarke/cdap,hsaputra/cdap,mpouttuclarke/cdap,caskdata/cdap,hsaputra/cdap,chtyim/cdap,chtyim/cdap,anthcp/cdap,anthcp/cdap,chtyim/cdap,anthcp/cdap,mpouttuclarke/cdap,mpouttuclarke/cdap,caskdata/cdap,hsaputra/cdap,hsaputra/cdap,caskdata/cdap,anthcp/cdap,hsaputra/cdap,chtyim/cdap,caskdata/cdap,anthcp/cdap,caskdata/cdap,chtyim/cdap,chtyim/cdap,caskdata/cdap