sysctl: print dotted keys again

When the globbing update was put into sysctl, you could no longer
simply use the keys because one key could potentially be
multiple paths once the glob expansion occured.  Using the path
instead gave a unique output.

Except certain programs, such as salt, expected the output to use
the dotted path "kernel.hostname" and not "kernel/hostname".

We can no longer use the original key, so now for each path:
  Copy the path
  strip off /proc/
  convert all / to .

The sysctl testsuite was also updated to check for a few different
types of conversion failures.

References:
 commit 6389deca5b
 https://www.freelists.org/post/procps/some-procpsn4400-fixes,4
 https://repo.saltproject.io/

Signed-off-by: Craig Small <csmall@dropbear.xyz>

NEWS

@@ -3,6 +3,7 @@ procps-ng-NEXT
     Re-add elogind support                                 merge #151
   * ps: threads again display when -L is used with -q      issue #234
   * ps: proper aix format string behavior was restored
+  * sysctl: print dotted keys again
 
 procps-ng-4.0.0
 ---------------