fix a collision betwen --ami command line param and env
fix a collision betwen --ami command line param and env

sysconfig scylla-server includes an AMI, the script also used an AMI
variable fix this by renaming the script variable

6a18634f9fcfb2abc14b56af3d904de9dcd1ac25 introduced this issue since it
started imported the sysconfig scylla-server

Signed-off-by: Shlomi Livne <6f01bf2e882e3bb6371d28d1418e5f729e7183e6@scylladb.com>
Message-Id: <0bc472bb885db2f43702907e3e40d871f1385972.1458767984.git.6f01bf2e882e3bb6371d28d1418e5f729e7183e6@scylladb.com>

duarten/scylla,raphaelsc/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,raphaelsc/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla