Renaming 'get_cmd_switch' and 'get_cmd_arg' to 'have_cmd_arg' and
'cmd_arg' respectively blends in nicely with the now omnipresent pattern
with 'have_[spec|board|installed|include]'.
This commit deprecates 'get_cmd_switch' and 'get_cmd_arg', which will be
removed in a later commit.
Issue #5432
Also remove 'requires_installation_of', while also checking sbin
directories in 'have_installed'. The run scripts have been adjusted
accordingly.
Fixes#2853