Setup connect timeout in curl.

Now curl will try to connect to docker daemon no longer then 10 seconds.
Remove debug printing.
Fix building with g++ 4.7.

G++ 4.7 removes default assignment operator from http_headers_t because of defined move constructor. Now i have defined assignment operators explicitly.
Docker plugin doesn't pool images by default.

If a user didn't specify registry in profile then the plugin will not pool images at all (will work with local images only).
Before it pooled images from dotCloud's registry and i think that this is a bad idea for a private cloud.
Avoid potential segmentation fault in docker client.

Before i filled libcurl's headers list as follows: append each header to vector and add pointer to content of the header in the vector to headers list.
But vector may reallocate memory when new items are added, that may invalidate some pointers in headers list.