fbcode_builder: getdeps: add run_cmd() function
fbcode_builder: getdeps: add run_cmd() function

Summary:
This runs a command, raising an exception if it exits with a non-zero error status.

It prints out the arguments in a mostly copy-and-pasteable form, with PATH-like
env vars pretty printed to make it easier to see what is being invoked; here's
an example of how cmake is being invoked later in this stack:

```
 ---
+ CMAKE_PREFIX_PATH=\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/ninja-5d7ec7:\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/cmake-91dc9a:\
+ PKG_CONFIG_PATH=\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/ninja-5d7ec7/lib/pkgconfig:\
+      /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/cmake-91dc9a/lib/pkgconfig:\
+ cd /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/build/zstd-470344 && \
+ cmake configure /data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/repos/github.com-facebook-zstd.git/build/cmake -DCMAKE_INST
ALL_PREFIX=/data/users/wez/scratch/dataZusersZwezZfbsource/fbcode_builder_getdeps/installed/zstd-470344 -DBUILD_SHARED_LIBS=OFF -DCMAKE_BUILD_TYPE=R
elWithDebInfo -G Ninja
```

Reviewed By: simpkins

Differential Revision: D14690999

fbshipit-source-id: cdb0c681c7dfdfdc6e8c96bf4830bfbcf666411b

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift