getdeps: Add support for brew packages and define package dependencies

Summary:
In order to speed up build times on a mac, add homebrew support to
getdeps.

Homebrew packages can be declared in a manifest using the `homebrew` header.

Futher, ahornby has added manifest entries for homebrew packages which are
included in this diff and also included a change to use the correct version of
openssl. Without this openssl change, homebrew cmake configure finds an old
openssl 1.0.2 install.

This diff provides a 2x speed up for building folly:

Timings for clean getdeps folly build on mid-2018 2.9Ghz i9 6 core intel macbook pro with 32GB RAM:

With new homebrew system deps:
```
rm -rf /Users/ahornby/.scratch/UsersZahornbyZfbsource/fbcode_builder_getdeps/
time ./opensource/fbcode_builder/getdeps.py build --allow-system-packages folly
real	17m39.329s
user	76m10.317s
sys	5m50.163s
```

Without:
```
rm -rf /Users/ahornby/.scratch/UsersZahornbyZfbsource/fbcode_builder_getdeps/
time ./opensource/fbcode_builder/getdeps.py build folly
real	32m10.344s
user	105m53.448s
sys	15m57.858s
```

Reviewed By: ahornby

Differential Revision: D33842632

fbshipit-source-id: ac785d4a8dcfa31b77292bddd9e747022ac36e3b

build/fbcode_builder/getdeps.py

@@ -415,6 +415,11 @@ class InstallSysDepsCmd(ProjectCmdBase):
             packages = sorted(set(all_packages["deb"]))
             if packages:
                 cmd_args = ["apt", "install", "-y"] + packages
+        elif manager == "homebrew":
+            packages = sorted(set(all_packages["homebrew"]))
+            if packages:
+                cmd_args = ["brew", "install"] + packages
+
         else:
             host_tuple = loader.build_opts.host_type.as_tuple_string()
             print(