fix dynamic link path for envs in shell and add async poll in pipe

[yunwei37]

Now, if the command file is link to relative path, it can be run from shell directly.

• if the command file is link to abstract path...I'm trying to figure it out in the rcore-fs.

other

• add async_poll for pipe

[coveralls]

Pull Request Test Coverage Report for Build 209780179

• 25 of 25 (100.0%) changed or added relevant lines in 4 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 46.578%

---

Files with Coverage Reduction	New Missed Lines	%
linux-object/src/fs/pipe.rs	1	87.18%
../../../../../usr/share/rust/.cargo/git/checkouts/rcore-fs-7fdf258332f6146d/517af47/rcore-fs/src/vfs.rs	4	8.51%

Totals
Change from base Build 208768481:	0.2%
Covered Lines:	6506
Relevant Lines:	13968

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 209780179

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 25 of 25 (100.0%) changed or added relevant lines in 4 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 46.578%

---

Files with Coverage Reduction	New Missed Lines	%
linux-object/src/fs/pipe.rs	1	87.18%
../../../../../usr/share/rust/.cargo/git/checkouts/rcore-fs-7fdf258332f6146d/517af47/rcore-fs/src/vfs.rs	4	8.51%

Totals
Change from base Build 208768481:	0.2%
Covered Lines:	6506
Relevant Lines:	13968

---

💛 - Coveralls