Remove non-portable source commands

`source(1)` is a bashism and is equivalent to the portable `.(1)`, but
as each commond is run in a new shell, spawning a shell to source a file
and exit is at best noop.

Some SUT used by acceptance tests do not use bash(1) as the default
shell, which cause CI failures because `source(1)` is not a valid
command.

Because we set variables in profile files, assume they are sourced
during shell startup will be available to next spawned shells.

spec/spec_helper_acceptance_local.rb

@@ -27,9 +27,7 @@ def export_locales(locale)
   LitmusHelper.instance.run_shell("echo export LANGUAGE=#{locale} >> /etc/profile.d/my-custom.lang.sh")
   LitmusHelper.instance.run_shell('echo export LC_COLLATE=C >> /etc/profile.d/my-custom.lang.sh')
   LitmusHelper.instance.run_shell("echo export LC_CTYPE=#{locale} >> /etc/profile.d/my-custom.lang.sh")
-  LitmusHelper.instance.run_shell('source /etc/profile.d/my-custom.lang.sh')
   LitmusHelper.instance.run_shell('echo export LC_ALL="C" >> ~/.bashrc')
-  LitmusHelper.instance.run_shell('source ~/.bashrc')
 end
 
 def pre_run