Provide the option to specify which search engines to use

[Hainish]

This is useful for https://github.com/EFForg/https-everywhere, see issue EFForg/https-everywhere#7277 (comment)

With this, we can specify what search engines to use - best configuration in our case is

python sublist3r.py -d example.com -e Baidu -e Yahoo -e Google -e Bing -e Ask -e Netcraft -e Virustotal -e "SSL Certificates"

[Hainish]

In the default configuration, all engines are used.

[the-st0rm]

I don't mind to merge that pull. The only thing I am not really comfortable with is the eval() you are using. I would probably create just a dictionary and do mapping between the engines and the actual objects.

I will still also discuss this with @aboul3la and see ig that affect the tool from any other perspective.

Thanks a lot for the pull request though :)

[Hainish]

@the-storm: I definitely get that. The reason why I considered it acceptable in this case is because the conditionals effectively whitelist what will ever pass through to the eval statement. I can open another PR following your suggestion if you like, though.

[the-st0rm]

@Hainish I think that would be very good. So I can merge the PR right away :)

[Hainish]

@the-st0rm: done

[aboul3la]

Hello @Hainish,

Thanks for your PR. We're glad to support EFF and https-everywhere.

I just have some few suggestions to improve this PR before I can merge it.

1. I don't think it's good to use many if conditions hard-coded inside the code. I think the optimal way is to use a dict that stores all the possible engines and match the user input against it.
2. it's better to use a comma separated list for the engine argument rather than using multiple -e args such as-e yahoo,google,bing,baidu it would be better than doing -e yahoo -e google -e bing -e baidu
3. It's better to use case insensitive matching for the engines names. As your current code will only work if the argument is like -e Yahoo but it won't work if it's -e yahoo

Below is a little code snippet i wrote on how the code should be:

    supported_engines = {'baidu':BaiduEnum,
                         'yahoo':YahooEnum,
                         'google':GoogleEnum,
                         'bing':BingEnum,
                         'ask':AskEnum,
                         'netcraft':NetcraftEnum,
                         'dnsdumpster':DNSdumpster,
                         'virstotal':Virustotal,
                         'threatcrowd':ThreatCrowd,
                         'ssl':CrtSearch,
                         'passivedns':PassiveDNS
                         }

    chosenEnums = []

    if engines == None:
        chosenEnums = [BaiduEnum, YahooEnum, GoogleEnum, BingEnum, AskEnum,
                       NetcraftEnum, DNSdumpster, Virustotal, ThreatCrowd, CrtSearch, PassiveDNS]
    else:
        engines = engines.split(',')
        for engine in engines:
            if supported_engines.has_key(engine.lower()):
                chosenEnums.append(supported_engines[engine.lower()])

Kindly update the PR so I can merge it.
Thanks

[Hainish]

@aboul3la: Thanks for the words of support! I've updated this PR.

[aboul3la]

Thank you @Hainish. It's merged now

[Foorack]

@aboul3la This breaks Python3 compatibility because 'has_key' function was removed in Python 3.