Allow starting program remotely

[bhecquet]

Expose a way to start a program on grid node
Use cases are business applications, soap ui, ...

NodeTaskServlet will serve this action

On start, grid reads all environment variables and searchs for SELENIUM_TOOL_ prefixed variables.
Grid record the name (without prefix) which is the tool name that will be exposed to clients and the value which is the path to executable

These tools will be added as capabilities to slots
CustomCapabilityMatcher will have to take tools into account when selecting slot

Servlet exposes "startProgram" action with 2 parameters:

• name: the name of the program to start (the one referenced in environment variables)
• params: parameters to add to program start
  It also records program PID so that it can be killed
  It returns an ID

Servlet exposes "stopProgram" action with 1 parameter:

• id: the id of the program to stop
  It uses the recorded PID to stop program

When stopping session, all remaining running programs are stopped

[bhecquet]

Won't be done