Optimized integration test case DockerSuite.TestBuildUsersAndGroups for #19425

Removed unnecessary RUN statements and combined some of the RUN statement into a single line.

The runtime performance is seen as follows:
pre-change:
PASS: docker_cli_build_test.go:3826: DockerSuite.TestBuildUsersAndGroups
63.074s

post-change:
PASS: docker_cli_build_test.go:3826: DockerSuite.TestBuildUsersAndGroups
49.698s

Signed-off-by: Anil Belur <askb23@gmail.com>