[cling-cpt] Replaced subprocess.popen calls with os.popen calls [skip-ci]

[saisoma123]

This Pull request: Replaced the subprocess.popen calls with os.popen calls. Using the os module in general will make build time faster.

Changes or fixes: Replaced 11 subprocess.popen calls with os.popen calls, so with my previous pull request regarding the subprocess calls and this one, this entirely replaces the subprocess module use in the cpt.

Checklist:

• tested changes locally
• [NA] updated the docs (if necessary)

This PR fixes the issue mentioned in #406 (root-project/cling#406)

[phsft-bot]

Can one of the admins verify this patch?

[vepadulano]

Why are these changes needed? In general it is recommended to switch from os to subprocess, not the other way around

[saisoma123]

That is correct, but I was told to replace the subprocess module use in the cpt, so I resorted to using the os module. I noticed however that the build time was quite a bit faster than before.

[vgvassilev]

That is correct, but I was told to replace the subprocess module use in the cpt, so I resorted to using the os module. I noticed however that the build time was quite a bit faster than before.

The idea behind the replacement was where possible. For example when we use subprocess to call tar or wget which have the relevant python support.