Update Dockerfile and streamline build steps #2274

Job	Run time
build-all	3m 7s
tests (scylla, -Pscylla-murmur -Dtest="*/core/cql/", murmur-core-java8, 8)	4m 30s
tests (scylla, -Pscylla-murmur -Dtest="*/hadoop/", murmur-hadoop-java8, 8)	11m 59s
tests (scylla, -Pscylla-murmur -Dtest="*/graphdb/cql/", murmur-graphdb, -Pjava-11, 11)	55m 43s
tests (scylla, -Pscylla-murmur -Dtest="*/graphdb/cql/", murmur-graphdb-java8, 8)	58m 19s
tests (scylla, -Pscylla-murmur -Dtest="*/core/cql/", murmur-core, -Pjava-11, 11)	4m 22s
tests (scylla, -Pscylla-murmur -Dtest="*/diskstorage/cql/", murmur-diskstorage-java8, 8)	15m 10s
tests (scylla, -Pscylla-murmur -Dtest="*/diskstorage/cql/", murmur-diskstorage, -Pjava-11, 11)	15m 35s
tests (scylla, -Pscylla-murmur -Dtest="*/hadoop/", murmur-hadoop, -Pjava-11, 11)	11m 38s
	3h 0m 23s

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