[check-http] Add --max-redirects option

[nonylene]

check-http cannot check redirects currently since http.Client follow redirects by default.

In this PR, I added --max-redirects option (like --max-redirs in curl or --max-redirect in wget) by setting client.checkRedirect.

Example

$ ./mackerel-check http --help
Usage:
 mackerel-check [OPTIONS]

Application Options:
 -u, --url=                  A URL to connect to
 -s, --status=               mapping of HTTP status
     --no-check-certificate  Do not check certificate
 -i, --source-ip=            source IP address
 -H=                         HTTP request headers
 -p, --pattern=              Expected pattern in the content
     --max-redirects=        Maximum number of redirects followed (default: 10)

Help Options:
 -h, --help                  Show this help message

$ ./mackerel-check http --max-redirects=1 -u http://mackerel.io/
HTTP OK: HTTP/1.1 200 OK - 35343 bytes in 5.142627 second response time

$ ./mackerel-check http --max-redirects=0 -u http://mackerel.io/
HTTP OK: HTTP/1.1 301 Moved Permanently - 178 bytes in 0.008557 second response time

[susisu]

LGTM! Thank you.