azdev setup: show error if pip command fails

[jiasli]

The current azdev setup silences any error that happens. This leads to difficulties in troubleshooting installation dependencies (#274, Azure/azure-cli#16655, Azure/azure-cli#16611).

• This PR lets pip_cmd raise CommandError by default if pip command fails. For other references of pip_cmds, they assume that pip_cmd succeeds. Now in case of failure, bare exception CommandError is raised.
• az setup now supports --verbose to show the commands that are run, --debug to show the command output.

azdev setup -c --debug

=======================
| Azure CLI Dev Setup |
=======================

Azure CLI:
    D:\cli\azure-cli


 Installing packages
=====================

Upgrading pip...
INFO: Running: D:\cli\env39\Scripts\python -m pip install --upgrade pip
DEBUG: Requirement already satisfied: pip in d:\cli\env39\lib\site-packages (21.0)
Collecting pip
  Using cached pip-21.0-py3-none-any.whl (1.5 MB)
  Using cached pip-20.3.4-py2.py3-none-any.whl (1.5 MB)

Installing `requirements.txt`...
INFO: Running: D:\cli\env39\Scripts\python -m pip install -r D:\cli\azure-cli\requirements.txt
DEBUG: Requirement already satisfied: setuptools==52.0.0 in d:\cli\env39\lib\site-packages (from -r D:\cli\azure-cli\requirements.txt (line 2)) (52.0.0)
Requirement already satisfied: pip>=9.0.1 in d:\cli\env39\lib\site-packages (from -r D:\cli\azure-cli\requirements.txt (line 3)) (21.0)

...

Installing `requirements.py3.Windows.txt`...
INFO: Running: D:\cli\env39\Scripts\python -m pip install -r D:\cli\azure-cli\src\azure-cli\requirements.py3.Windows.txt
ERROR: Command `D:\cli\env39\Scripts\python -m pip install -r D:\cli\azure-cli\src\azure-cli\requirements.py3.Windows.txt` failed with exit code 1:
...
  _openssl.c
  build\temp.win-amd64-3.9\Release\_openssl.c(575): fatal error C1083: Cannot open include file: 'openssl/opensslv.h': No such file or directory
  error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.28.29333\\bin\\HostX86\\x64\\cl.exe' failed with exit code 2
  ----------------------------------------
  ERROR: Failed building wheel for cryptography
  ...

[jiasli]

Use the better function os.path.join in lieu of / join to avoid non-standard path separator on Windows:

D:\cli\azure-cli/requirements.txt -> D:\cli\azure-cli\requirements.txt
                ^                                    ^