If thinking about life in general, Logic would suggest that it was an inevitability. Believing in a set path: Since it has happened, then it was going to happen and that makes it an inevitability. Believing in many paths: Also, if it is even simply a possibility, then if that possibility exists then again in the span of eternity, it is an inevitability. We know it is an option because here it is, existing. So to sum up, it is in most considerations an inevitability. (why was life inevitable is another discussion)
However if we think about life on Earth specifically as an inevitability, then there might be more debate. Certainly if you believe in God, then it is an inevitability that Earth would have life. But if you don't, then it is up to if theories of life developing in an evolutionary fashion are actually true. If they are or if some other process of self-developing life is true, then it is not an inevitability that Earth would have life, but it is also not a fluke due to the reasons mentioned in the first paragraph. Life would have eventually begun on some planet at some time and Earth was one to aquire it. Since it did, then the situations were more right for Earth to acquire life than many other planets, therefore by statistics and probability it cannot be a fluke.
So to sum up both paragraphs: It may or may not have been an inevitability, but it cannot be a fluke.
