spack ci rebuild: Don't install in a login shell

On some systems the shell in login mode wipes important parts of the
environment, such as PATH. This causes the build to fail since it can't
find `spack`.

For better robustness, don't use a login shell.

lib/spack/spack/cmd/ci.py

@@ -491,10 +491,9 @@ def ci_rebuild(args):
     install_copy_path = os.path.join(repro_dir, 'install.sh')
     shutil.copyfile('install.sh', install_copy_path)
 
-    # Run the generated install.sh shell script as if it were being run in
-    # a login shell.
+    # Run the generated install.sh shell script
     try:
-        install_process  = subprocess.Popen(['bash', '-l', './install.sh'])
+        install_process  = subprocess.Popen(['bash', './install.sh'])
         install_process.wait()
         install_exit_code = install_process.returncode
     except (ValueError, subprocess.CalledProcessError, OSError) as inst: