Avoid "Text file busy" error after chmod

[jonekdahl]

I had the problem detailed in moby/moby#9547 when building the image:

Step 21 : RUN chmod +x /*.sh && ./configure.sh
 ---> Running in 636c9f13df4e
/bin/sh: 1: ./configure.sh: Text file busy
INFO[0000] The command [/bin/sh -c chmod +x /*.sh && ./configure.sh] returned a non-zero code: 2 

By inserting a short sleep between the chmod and the execution of configure.sh, the issue was resolved.

[jonekdahl]

I guess this is not needed any longer since #8 was merged.

[ivantopo]

@jonekdahl thanks for taking the time for proposing this PR and also for the follow up! I'm sorry I didn't jump in before, to be honest, we are not currently using this docker image and it makes it more difficult to decide whether something should go in or not. Hope you find it useful, regards!