[tetrapak] Add possibility for context have many directories

Summary:
It is needed, because only one context can exists at the time, and context have only one directory.
It was not possible to have many different directories. Some times it is needed for running the tasks on different
directories( for example for tetrapak_deps plugin). And it was implemented with starting extra OS process(extra erlang vm per every erlang dependency).

With this change it is possible to implement handling of other erlang applications within the same erlang VM, as the same context can hadle different directories and separate tasks and task dependencies between them.

Test Plan: make, read, test tetrapak_deps (coming soon)

Reviewers: vtarasen, aschultz, orixmann

Reviewed By: vtarasen

CC: mkraemer, aschultz

Differential Revision: https://review.tpip.net/D1238
[tetrapak] separate config/results between other directories

Summary:
started in D1238 changes for separating of tasks contextes, needs the separation
for a result variables and configuratioтs too.

Test Plan: make, read

Reviewers: vtarasen, aschultz, orixmann

Reviewed By: vtarasen

CC: mkraemer, aschultz

Differential Revision: https://review.tpip.net/D1240
[tetrapak] add tetrapak:load task, required before all tasks, that working with application (info, build, check, shell, start)

Summary: It must be common place to trigger some modifications, that are needed for working oк starting applications in all cases, like tests, shell, start, info

Test Plan: make, read

Reviewers: vtarasen, orixmann, aschultz

Reviewed By: vtarasen

CC: mkraemer, aschultz

Differential Revision: https://review.tpip.net/D1241
[tetrapak] add_directory doesn't remove old tasks

Summary: For a case, if it will be initialized twice, the tasks are not removed. The tasks were overwritten before. Now, it is possible to go with a normal procedure throw a normal register_tasks procedure. Register tasks merge the registered tasks before and new one. If there are tasks presented. There will be nothing happen.

Test Plan: make, read

Reviewers: orixmann, aschultz, vtarasen, hsychla

Reviewed By: hsychla

CC: mkraemer, aschultz

Differential Revision: https://review.tpip.net/D1245