pw_env_setup: allow setting environment directory

Allow setting of environment installation directory. Everything created
from environment setup gets installed into this directory.

The first time bootstrap is run after this commit is applied will take
longer, and eventually the old paths should be removed from .gitignore
(and deleted).

Bug: 216
Change-Id: I92ebe8a2414998cb5e4ae9ef3a92d6b50ffa8fab
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/13600
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Rob Mohr <mohrr@google.com>
diff --git a/.gitignore b/.gitignore
index 4f09cea..87f69cb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,7 +3,6 @@
 out/
 bazel-*
 .presubmit/
-.bootstrap/
 
 # Editors
 .idea/
@@ -15,9 +14,6 @@
 *.swo
 
 # Python
-python*-env/
-.python*-env/
-venv/
 *.pyc
 *.egg/
 *.eggs/
@@ -47,10 +43,17 @@
 *_REMOTE_*.txt
 
 # Env Setup
+environment
+.environment
+# TODO(pwbug/216) Remove following lines in this section.
+# Maybe find a way to delete these files before these lines are removed.
+python*-env/
+.python*-env/
 pw_env_setup/.env_setup.sh
 pw_env_setup/.env_setup.bat
 .cipd
 .cargo
+.bootstrap/
 
 # Web Tools
 node_modules