Hey guys,
This isn’t a problem per say since I already found the answer to my problem. But I thought I should contribute it here so that others that might run across the same problem will find a reference to it.
While trying to build an image for our production images based on the cents:7 docker base image, I got ‘permission denied’ when the composer was running the post install commands. The permission denied was happening when the “bin/grav install” command was attempted. Turns out the permissions on the files in the bin directory were not allowing execution. Here is a sample from my docker build:
Generating autoload files
> bin/grav install
sh: bin/grav: Permission denied
Script bin/grav install handling the post-create-project-cmd event returned with error code 126
The command ‘/bin/sh -c php composer.phar create-project getgrav/grav /webroot/grav 1.3.10’ returned a non-zero code: 126
After searching for a while without much luck, I found an unrelated article explaining a problem related to php+zip decompression that could cause permissions to be wrong. This link provided the hint:
https://github.com/composer/composer/issues/4471
I added a docker step to install unzip thru yum and voila it works. My docker build now installs cleanly with grav installing thru the composer properly.
Now on to the next steps 
Jeff