feat: allow tests to be run in other places than /tmp

[theguy147]

feat: allow tests to be run in other places than /tmp

Description/Motivation/Screenshots

Today I tested GEF on a non-rooted Android device and had to manually make quite some changes to have the tests run because I didn't have access to the tmp/ filesystem.

This PR allows changing the defaults for TMPDIR (where the binaries are compiled to and used for the tests and where trace-run saves the traces while testing) by setting an environment variable for easier testing in different environments.

Changes:

• Allow changing TMPDIR by using an environment variable of the same name instead of having hard coded paths for testing (default is still /tmp as before).
• Don't copy gef.py to TMPDIR but leave it in-place for testing (because there doesn't seem to be a need to copy it over)
• Allow changing GEF_PATH by using an environment variable to use quickly switch between different gef.py versions without VCS (useful for automated testing of different GEF versions)
• Makefile targets are set to .PHONY now
• Create TMPDIR if it doesn't exist
• Remove cleaning steps from test target in Makefile so e.g. the binaries don't need to be rebuild between every test run (instead introduce separate clean target).
• Allow running single test modules with e.g. make TestGefCommandsUnit (capitalized)
• Allow running single tests (or several) using patterns with e.g. make test_cmd_elf_info (specifically that one test) or make test_cmd_heap_ (every test starting with "test_cmd_heap")

EDIT:

• Allow debugging tests on failure by setting DEBUG environment variable: DEBUG=1 make test
• get_shellcode() now saves the downloaded shellcode to gef.tempdir instead of a hardcoded /tmp

How Has This Been Tested?

Architecture	Yes/No	Comments
x86-32	✔️
x86-64	✔️
ARM	✖️
AARCH64	✖️
MIPS	✖️
POWERPC	✖️
SPARC	✖️
RISC-V	✖️
make test	✔️

Checklist

• My PR was done against the dev branch, not master.
• My code follows the code style of this project.
• My change includes a change to the documentation, if required.
• My change adds tests as appropriate.
• I have read and agree to the CONTRIBUTING document.

[hugsy]

Pretty awesome