Don't exit on errors

[Crevil]

Describe the bug
We see that the exporter exits regularly due to some intermediate errors or issues at the Snyk APIs. This is generally an odd behaviour and should instead just be logged, as the exporter is not failing in its operation.

Here is a common error we see due to connection closing:

Get https://snyk.io/api/v1/org/UUID/projects: read tcp IP:36810-\u003eIP:443: read: connection reset by peer

To Reproduce

Add a test case for above error to TestPoll.

{
	name: "tcp connection reset by peer",
	collectorErr: &url.Error{
		Op:  "GET",
		URL: "/url",
		Err: &net.OpError{
			Op:  "read",
			Net: "tcp",
			Addr: &net.IPAddr{
				IP: net.IPv4zero,
			},
			Err: &net.OpError{
				Op:  "read",
				Err: syscall.ECONNRESET,
			},
		},
	},
	output: nil,
},

Expected behavior
The error should just be logged as above but the application should keep on running.

Application (please complete the following information):

• Distribution: Docker image
• Version 1.4.0

Log output (if applicable):

{"level":"error","msg":"Snyk exporter exited due to error: organization NAME (UUID): Get https://snyk.io/api/v1/org/UUID/projects: read tcp IP:36810-\u003eIP:443: read: connection reset by peer","source":"main.go:121","time":"2019-10-04T10:08:23Z"}

[Crevil]

Related to #13 and #14

By implementing above mentioned functionality we can get rid of all the special handling of errors.