Use composer as root for install

[JedMeister]

Work around turnkeylinux/tracker#1960 - by running composer as root, rather than using turnkey-composer.

[OnGle]

Bizarre, how does this fix the issue?

[JedMeister]

Yes it is bizarre! Very bizarre!

Apologies if the issue wasn't clear enough.

In an effort to make the issue clearer, I've updated the bug with this (2nd) paragraph:

The issue is that it's timing out downloading the flex json file. The install works fine up until that point. Clearly that is a 404 download error, but it occurs consistently when using turnkey-composer. For some very strange and unknown reason, running composer as root (as per [link to this PR]) works fine?!

The issue is worth investigating further, but I'd really like to publish Symfony ASAP.

[JedMeister]

Actually, just added a bit more info to the issue:

Initially I thought it might have been a squid (proxy) problem, but I tried clearing the squid cache and same result. It's reproducible on another TKLDev.

[OnGle]

Well that's weird but lgtm!