Fix issue; node roles are defaulting to true when undefined (false) breaking usage of nodeFilter option

[deuscapturus]

nodeFilter option was unable to filter nodes where master, data or ingest roles were false because they were defaulting to true when not set.

The example below demonstrates the problem:

// roles are returned from the elastic API as a list
roleslist = ['master', 'ingest']
console.log(roleslist)

// The client converts the list to a dictionary
const roles = roleslist.reduce((acc,role) => { acc[role] = true; return acc}, {})
console.log(roles)

// The client then assigns default values to undefined roles
console.log(
        Object.assign({'data': true, 'master': true, 'injest': true, 'ml': false}, roles)
)

Output:

[ 'master', 'ingest' ]
{ master: true, ingest: true }
{ data: true, master: true, injest: true, ml: false, ingest: true }

data is true when it should be false.

[delvedor]

Hello! Thank you for the PR!
You are right, this is a bug.
Can you also add a unit test?

[deuscapturus]

tests added

[deuscapturus]

oops. I hijacked another test. Let me try something different...

[delvedor]

LGTM

[delvedor]

jenkins run the tests please

[niksrc]

@delvedor any reason this change is not released for @elastic/elasticsearch@5 yet?