Set default Agent's initial maxSockets to 1

[natevw]

The new rationale here is that:

• the lower, the better as far as current CC3K stack goes
• this may also make it a little clearer where the problem lies in situations like #674, than the previous value of 2

@LinusU how does this sound as a replacement for #675?

[LinusU]

I think 1 is sane since we have such a limited number of connections on the tessel.

The only downside is not being able to make parallel http requests. I guess it would be very cool if socket queueing could be handled at an lower level which would allocate sockets to the different parts (net/dgram/http, Server/Client). A program recording data from senors and sending to different apis would get 3 http.Client and 1 dns socket. A small web server would get 4 sockets for incoming connections. I guess it might be a bit complicated to figure out how it should work thought...

LGTM

@johnnyman727 is switching to the CC3100 on the roadmap?

[natevw]

Sounds like everyone's content with this then? Can someone r+.

@LinusU Users are still welcome to e.g. require('http').globalAgent.maxSockets = 4 (or provide an equivalent agent to all requests) if they would like a different setting for their app; we're just aiming for the best "out-of-box" default here.

[johnnyman727]

@natevw can we rebase the first commit out of this PR for cleanliness?

[tm-rampart]

Approved by @tcr. Running tests.