Remove indentation in process errors. (#10181)
Remove indentation in process errors. (#10181)

### Problem

`dedent` was failing due to interpreting the stdio content of the failed process, leading to deeply indented output:
```
23:45:13 [ERROR] 1 Exception encountered:

Engine traceback:
  in `lint` goal
  in Lint using Flake8
Traceback (most recent call last):
  File "/Users/stuhood/src/pants/src/python/pants/engine/process.py", line 215, in fallible_to_exec_result_or_raise
    description.value,
pants.engine.process.ProcessExecutionFailure:                 Process 'Building flake8.pex with 4 requirements: flake8-2020>=1.6.0,<1.7.0, flake8-pantsbuild>=2.0,<3, flake8>=3.7.9,<3.9, setuptools<45' failed with exit code 1.
                stdout:


                stderr:
                ERROR: Could not find a version that satisfies the requirement flake8-2020<1.7.0,>=1.6.0 (from versions: none)
ERROR: No matching distribution found for flake8-2020<1.7.0,>=1.6.0
```

### Solution

Switch to using join on unformatted strings.

### Result

```
23:57:18 [ERROR] 1 Exception encountered:

Engine traceback:
  in `lint` goal
  in Lint using Flake8
Traceback (most recent call last):
  File "/Users/stuhood/src/pants/src/python/pants/engine/process.py", line 215, in fallible_to_exec_result_or_raise
    description.value,
pants.engine.process.ProcessExecutionFailure: Process 'Building flake8.pex with 4 requirements: flake8-2020>=1.6.0,<1.7.0, flake8-pantsbuild>=2.0,<3, flake8>=3.7.9,<3.9, setuptools<45' failed with exit code 1.
stdout:

stderr:
ERROR: Could not find a version that satisfies the requirement flake8-2020<1.7.0,>=1.6.0 (from versions: none)
ERROR: No matching distribution found for flake8-2020<1.7.0,>=1.6.0
```

[ci skip-rust-tests]

jsirois/pants,pantsbuild/pants,jsirois/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,jsirois/pants