Editable dependencies have a race condition when installing
When installing editable dependencies, they must update `site-packages/easy-install.pth` with the path to the src of the repo checkout, for it to be able to be imported. By default pipenv installed all dependencies in blocks that run concurrently, but since multiple editable installs edit the same file this creates a race condition where multiple files may be trying to edit at the same time, resulting in some not being included.

In about 10 runs of `pipenv install` with the Pipfile below, 4 only included the second (variant) path, 2 only included the first (affect) path, and 4 included both paths. This can be worked around using `--sequential` at the cost of installs being much slower.

Ideally, pipenv could gather all editable dependencies and run them all sequentially at the end of the install process so as to not cause the race condition.

Python 2.7
Pipenv 8.2.7

Pipfile:
```
[[source]]
url = "https://pypi.python.org/simple"
verify_ssl = true
name = "pypi"

[dev-packages]

[packages]
django-affect = {ref = "master", git = "https://github.com/jsatt/django-affect.git", editable = true}
django-variant = {ref = "master", git = "https://github.com/jsatt/django-variant.git", editable = true}
```
diff --git a/pipenv/cli.py b/pipenv/cli.py
index 5b9c55e1..1586ea21 100644
--- a/pipenv/cli.py
+++ b/pipenv/cli.py
@@ -783,11 +783,11 @@ def do_install_dependencies(
                 del v['hash']
 
     # Convert the deps to pip-compatible arguments.
-    deps_list = [(d, ignore_hashes) for d in convert_deps_to_pip(deps, project, r=False, include_index=True)]
+    deps_list = [(d, ignore_hashes, blocking) for d in convert_deps_to_pip(deps, project, r=False, include_index=True)]
     failed_deps_list = []
 
     if len(vcs_deps):
-        deps_list.extend((d, True) for d in convert_deps_to_pip(vcs_deps, project, r=False))
+        deps_list.extend((d, True, True) for d in convert_deps_to_pip(vcs_deps, project, r=False))
 
     # --requirements was passed.
     if requirements:
@@ -798,7 +798,7 @@ def do_install_dependencies(
 
     deps_list_bar = progress.bar(deps_list, label=INSTALL_LABEL if os.name != 'nt' else '')
 
-    for dep, ignore_hash in deps_list_bar:
+    for dep, ignore_hash, block in deps_list_bar:
         if len(procs) < PIPENV_MAX_SUBPROCESS:
             # Use a specific index, if specified.
             index = None
@@ -814,7 +814,7 @@ def do_install_dependencies(
                 allow_global=allow_global,
                 no_deps=no_deps,
                 verbose=verbose,
-                block=blocking,
+                block=block,
                 index=index
             )
 
['pipenv/cli.py']