RRDtool dual process (remote creation/check) (#4104)

* Prepare for dual rrdtool processes
Disabled at this time
Split out rrdtool version checks into rrdtool_create_command()
Tests for rrdtool_create_command()
Fixes a few small issues.

* Enable dual process and remote rrd check/creation

* remove full path for remote commands

* Doc updates
minor fix to rrdtool_tune()

* Set up bootstrap for phpunit
Fix issues with FileExistsException

* Attempt to fix phpunit

* Fix classloader and bootstrap to use full paths only (not depending on $config)

* Fix phpunit tests, config.php does not exist.

phpunit.xml

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit colors="true">
+<phpunit colors="true" bootstrap="tests/bootstrap.php">
     <testsuites>
         <testsuite name="Application Test Suite">
-            <directory>./tests/</directory>
+            <directory>tests/</directory>
         </testsuite>
     </testsuites>
 </phpunit>