* miniconda - use a stable install path
Conda updates itself (as noted by the use of `auto_updates true`) so as noted by @janosh by installing into `staged_path` we end up using a path with the version number of the initial install of miniconda. So when we update conda with itself using:
```
$ conda update conda
```
We'll end up with a version that's different then the install path indicates which could cause confusion:
```
$ conda info --base
/usr/local/Caskroom/miniconda/4.6.14/miniconda3
$ conda --version
conda 4.7.10
```
This change uses `#{caskroom_path}/base` as the install path which gives us a nicer looking path for the base Conda env:
```
$ conda env list
base * /usr/local/Caskroom/miniconda/base
```
And it will be stable across Conda updates:
```
$ conda info
active environment : base
active env location : /usr/local/Caskroom/miniconda/base
shell level : 1
user config file : /Users/xyu/.condarc
populated config files :
conda version : 4.7.10
conda-build version : not installed
python version : 3.7.3.final.0
virtual packages :
base environment : /usr/local/Caskroom/miniconda/base (writable)
channel URLs : https://repo.anaconda.com/pkgs/main/osx-64https://repo.anaconda.com/pkgs/main/noarchhttps://repo.anaconda.com/pkgs/r/osx-64https://repo.anaconda.com/pkgs/r/noarch
package cache : /usr/local/Caskroom/miniconda/base/pkgs
/Users/xyu/.conda/pkgs
envs directories : /usr/local/Caskroom/miniconda/base/envs
/Users/xyu/.conda/envs
platform : osx-64
user-agent : conda/4.7.10 requests/2.22.0 CPython/3.7.3 Darwin/18.6.0 OSX/10.14.5
UID:GID : 501:20
netrc file : None
offline mode : False
```
* Add caveat about needing conda init to finish setup
In order to use Conda `conda init` must first be run in the user's interactive login shell. Add a caveat to inform users of this after install, this resolves#66490.
suschizu