Repository: conda/conda

Issue:
`conda update -n nonexistent --all` crashes


## Current Behavior
Running:

```
conda update -n non-existent-env --all
```

crashes with

```
    Traceback (most recent call last):
      File "/opt/anaconda/lib/python3.7/site-packages/conda/exceptions.py", line 1079, in __call__
        return func(*args, **kwargs)
      File "/opt/anaconda/lib/python3.7/site-packages/conda/cli/main.py", line 84, in _main
        exit_code = do_call(args, p)
      File "/opt/anaconda/lib/python3.7/site-packages/conda/cli/conda_argparse.py", line 82, in do_call
        return getattr(module, func_name)(args, parser)
      File "/opt/anaconda/lib/python3.7/site-packages/conda/cli/main_update.py", line 20, in execute
        install(args, parser, 'update')
      File "/opt/anaconda/lib/python3.7/site-packages/conda/cli/install.py", line 174, in install
        if args.mkdir:
    AttributeError: 'Namespace' object has no attribute 'mkdir'
```

## Environment Information
<details open><summary><code>`conda info`</code></summary><p>
<!-- between the ticks below, paste the output of 'conda info' -->

```
     active environment : default
    active env location : /opt/anaconda/envs/default
            shell level : 1
       user config file : /home/alan/.condarc
 populated config files : /home/alan/.condarc
          conda version : 4.8.3
    conda-build version : 3.19.1
         python version : 3.7.6.final.0
       virtual packages : __glibc=2.27
       base environment : /opt/anaconda  (writable)
           channel URLs : https://conda.anaconda.org/conda-canary/linux-64
                          https://conda.anaconda.org/conda-canary/noarch
                          https://conda.anaconda.org/conda-forge/linux-64
                          https://conda.anaconda.org/conda-forge/noarch
                          https://repo.anaconda.com/pkgs/main/linux-64
                          https://repo.anaconda.com/pkgs/main/noarch
                          https://repo.anaconda.com/pkgs/r/linux-64
                          https://repo.anaconda.com/pkgs/r/noarch
          package cache : /opt/anaconda/pkgs
                          /home/alan/.conda/pkgs
       envs directories : /opt/anaconda/envs
                          /home/alan/.conda/envs
               platform : linux-64
             user-agent : conda/4.8.3 requests/2.24.0 CPython/3.7.6 Linux/5.3.0-53-generic ubuntu/18.04.4 glibc/2.27
                UID:GID : 1000:1000
             netrc file : None
           offline mode : False
```
</p></details>


<details open><summary><code>`conda config --show-sources`</code></summary><p>
<!-- between the ticks below, paste the output of 'conda config --show-sources' -->

```
=> /home/alan/.condarc <==
channel_priority: strict
channels:
  - conda-canary
  - conda-forge
  - defaults
```
</p></details>


Discussion:

Resolving patch:
diff --git a/conda/cli/install.py b/conda/cli/install.py
--- a/conda/cli/install.py
+++ b/conda/cli/install.py
@@ -148,7 +148,7 @@ def install(args, parser, command='install'):
                 # fall-through expected under normal operation
                 pass
         else:
-            if args.mkdir:
+            if hasattr(args, "mkdir") and args.mkdir:
                 try:
                     mkdir_p(prefix)
                 except EnvironmentError as e:


Test patch: