PTDEBUG for shell tools

From bug 989951: Several Percona Toolkit scripts are using bash as programming language.

For them, PTDEBUG env var is not used, but sometimes it could be useful to know what the tool is doing (to debug things like bug 986151).

Adding the following line may provide a simple debug, to show everything executed :

if [ "$PTDEBUG" == "1" ]; then
   set -x
fi

This could be added in all bash scripts in Percona Toolkit.

OBSOLETE: If all PTDEBUG=1 does is set -x, then simple /bin/bash -x <tool>.